This invention relates to portable high performance medical amplifier, in particular to a pure digital medical amplifier for digitally acquiring, conditioning, storing, and transferring clinically and non-clinically applied biomedical signals.
Clinically and non-clinically applied biomedical signals, such as blood pressure, pulse, heartbeat, EEG, ECG, EMG, ERG, EOG, EGG, EP, ERP, AP, membrane potentials, ion potentials, ion currents, fluorescent currents, and optical electrical currents, are characterized by their low amplitude, and low frequency and near direct current signal components, usually below 30,000 Hz with major components in a range of 0.1-100 Hz.
The biomedical amplifiers been used widely both clinically and non-clinically nowadays are typically composed of the following stages: input buffer stage, pre-amplification stage, isolation amplification stage, high-pass filtering stage, low-pass filtering stage, notch filtering stage, post-amplification/attenuation stage, and output stage. The amplification gain is generally in the range from 1000 to 500000. The output amplitude is generally +/−0.1 to +/−10.0 volts, in order to meet the requirements such as display, measurement, recording, and acquisition of biomedical signals.
Such biomedical analog amplifiers described above have the following problems:
High internal noise, high signal distortion, and small dynamic range are the most serious problems. Multiple stages of amplification and filtering tend to generate much more internal noise than fewer stages because each stage contributes extra internal noise, and more peripheral electronic components also contribute more internal noise. Furthermore, multiple stages tend to consume more electric power and also add extra thermal noise. In addition, multiple stages need more circuit board space, the analog signal wires tend to be longer, and so are easier to introduce random noise as well as 50/60 Hz interference noise. Therefore, even a well designed analog medical amplifier typically suffers from internal noise level at 5-50 uV (RMS) or higher. As each stage causes analog signal distortion, an amplifier with multiple stages has significant signal distortion. When the amplification gain gets higher, the dynamic range of the amplifier becomes smaller. Commonly, the dynamic range of a biomedical amplifier with gain of 1000 is less than 10 mV, and that with gain of 500000 is less than 50 uV.
The filtering parameters are not changeable. The electronic filtering parameters are determined by the electronic components in the circuit, and cannot be changed once the amplifier is produced. For example, a notch filtering circuit designed for 50 Hz is not useable in the 60 Hz environment. The high-pass and low-pass filters are fixed once the amplifier design is over. This limits the versatile use of the amplifier for various applications, and the circuit must be specially designed in order to meet various filtering purposes.
There is no capability of signal processing and data analysis in these biomedical analog amplifiers. Analog signals can barely be processed and analyzed, and these signals need to be digitized before advanced processing and analysis can take place. The digitized biomedical signals often need various computations of signal processing and data analysis in real-time or non-real-time, such as low-pass filtering, high-pass filtering, notch filtering, data binning/insertion, data compression/decompression, data modulation/demodulation, time domain analysis, frequency domain analysis, waveform recognition, image processing, and result sorting. These computations require high performance digital signal controller in order to complete the tasks within few milliseconds. Currently various biomedical amplifiers are not capable of performing signal processing and data analysis.
The analog output from these biomedical analog amplifiers tends to worsen the signal quality, especially when output connection wire is long in distance and when connected device is contaminated with interference noise. High noise level, high distortion, small dynamic range, DC drifting, low efficiency, and high power consumption are typical in these amplifiers. To avoid interference noise introduced by a connected analog device, a linear photo isolator is often used, which further exacerbates the signal quality. Another approach been widely used to isolate the interference source is to modulate or digitize the biomedical signal, transfer the data via a digital photo isolator, and then demodulate or convert the data back to analog format for the next device. Unfortunately, this method suffers the same problems as these biomedical analog amplifiers with the cost of complicating the design and manufacturing.
The transferring efficiency is low for multiple channel biomedical signals. These analog amplifiers always use multiple connection wires for analog biomedical signal transferring. There is always signal cross talk between the parallel channels at certain degree, especially when the connection wire line is long. Furthermore, there is no way of compression for analog signals, and so the utilization of the signal transfer bandwidth is of low efficiency.
The signal transfer distance is limited. As the output of these analog amplifiers is in analog format, the signal quality degrades quickly with the transfer distance. If wireless approach is applied for long distance signal transfer, the analog signals must be modulated and then demodulated in order to achieve the signal transfer, and the signal quality will be affected. Currently only digitized signals can be transferred remotely with high fidelity and no loss.
The signals have poor security during transfer. Clinically applied biomedical signals may involve patient's sensitive information, and should be secured in general. However, analog signals are not easily encrypted and so cannot be effectively secured. This results in that the analog signals from analog biomedical amplifiers may be captured and abused during remote transfer, especially radio frequency transfer as the radio signal is aimlessly scattered in the space.